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Re: unreviewed patch: opt/7409
- From: Ulrich Weigand <weigand at immd1 dot informatik dot uni-erlangen dot de>
- To: rth at redhat dot com
- Cc: hpenner at de dot ibm dot com, uweigand at de dot ibm dot com, gcc-patches at gcc dot gnu dot org
- Date: Tue, 8 Oct 2002 21:20:45 +0200 (MET DST)
- Subject: Re: unreviewed patch: opt/7409
Richard Henderson wrote:
>The patch should not immediately set single_usage
>to const0_rtx. That should be done only if it is
>already non-null.
As I recall, the issue here is that marking a reg
as 'single_usage' means that the single usage can
be replaced by something else.
In the case of registers in CALL_INSN_FUNCTION_USAGE,
those registers are usually hardcoded by the ABI and
cannot by replaced.
So it might make more sense to immediately mark them
as 'multiple usage' even though this is not strictly
true. If not, the users of single_usage would need
to check for this case (and then don't do anything
anyway).
However, this would certainly be worth a comment ...
Bye,
Ulrich
--
Dr. Ulrich Weigand
weigand@informatik.uni-erlangen.de